Many environmental and endogenous factors can temporarily bind to DNA targets and inhibit gene transcription. Whether these factors induce DNA repair and targeted mutagenesis is largely unclear. In their previous studies, oligonucleotide triplex formation has been demonstrated to have the capability of inducing targeted mutagenesis in an SV40 viral vector. Triplex-mediated targeted mutagenesis has been further demonstrated to be related to DNA nucleotide excision repair and transcription-coupled repair. Since triplexes have been detected in mammalian genomic DNAs, this observation has raised the possibility that intracellular triplexes as well as other environmental and endogenous factors known to temporarily inhibit gene transcription may have the potential to induce TCR and cause targeted mutagenesis; furthermore, TCR-mediated targeted mutagenesis may contribute to genetic instability and lead to development of many human diseases including genetic diseases, cancer, neurodegenerative and aging-related diseases. Dr. Wang proposes to study the molecular mechanisms of transcription-coupled repair and the correlation between transcription-coupled repair and genetic instability using DNA triplex structure as a model system. Triplex-mediated transcription-coupled repair will be studied both in vitro and in vivo using human cells with different DNA repair background. Intracellular triplex structure-mediated genetic instability will be studied both in SV40 viral systems and in human cells carrying lambda shuttle vectors within chromosomes. The correlation between transcription-coupled repair and other DNA repair pathways such as nucleotide excision repair and mismatch repair also will be studied using different DNA repair-proficient and deficient human cells. The knowledge obtained from this project will provide an understanding of the molecular mechanisms of transcription-coupled repair and its contribution in genetic instability. The knowledge gained from this project also will lead to an understanding of whether many environmental and endogenous factors known only to inhibit gene transcription could induce targeted mutagenesis and result in genetic instability that might contribute to the development of many human diseases including genetic diseases, cancer, neurodegenerative and aging-related diseases. In long term, the understanding of transcription-coupled repair will have both scientific and clinical importance since the knowledge obtained from this project not only will benefit scientific research such as transcription regulation and DNA repair/replication but also may help to prevent development of many human diseases caused by intracellular triplexes and other environmental and endogenous factors.